WIRELESS APPARATUS

Abstract

 In one embodiment of the present invention, even if a radio apparatus 100 is small, it is possible to realize a high-efficiency antenna capacity by allowing an antenna 1, a circuit board 2 and a conductive line 3 to function as a whole as an antenna. The radio apparatus 100 in one embodiment of the present invention includes: the antenna 1 for transmitting and receiving radio waves of a wavelength λ; and the circuit board 2 connected to the antenna 1; the power supply 4; and the conductive line 3 for connecting together the circuit board 2 and the power supply 4, wherein a sum of a length of the antenna 1, a length of the circuit board 2 and a length of the conductive line 3 is about λ/2.

Description

TECHNICAL FIELD

[0001] The present invention relates to a radio apparatus. For example, the present invention relates to a radio apparatus attached to a meter unit such as a gas meter or an electricity meter, and to a radio apparatus for relaying radio waves transmitted or received by those meter units. For example, the present invention also relates to a radio apparatus for which there is a demand for reducing the size of the antenna and the circuit board.

BACKGROUND ART

[0002] Automatic meter reading systems have become widespread, which enable collection of data, via radio communication, of the amount of use from a gas meter or an electricity meter installed in a building such as a house or a condominium, instead of meter reading persons visiting every household. Since the wireless range of such automatic meter reading systems is dictated by the transmission power, the receiving sensitivity and the antenna capacity of the radio equipment, the systems therefore require a high radio communication capacity. Use of other systems has also started, which are capable of transmitting meter reading data inexpensively over greater distances by using relays, each including an antenna, a radio section and a microcomputer, in order to ensure the radio communication capacity. There is also a demand for reducing the weight and the size of meters and relays in view of the need for simplifying the installation and the need for finding places of installation.

[0003] Patent Document 1 proposes a technique of reducing the size of the apparatus while avoiding the deterioration of the antenna capacity by altering the electrical connection between the metal device and the main board.

[0004] With the antenna of Patent Document 1, the deterioration of the antenna capacity is avoided by altering the length of the connection pattern for electrically connecting the main board with a metal device other than the antenna, thereby shifting the unnecessary resonance due to the metal device out of the band. Moreover, since the device is not shielded, there is no deterioration of the antenna radiation property due to the ground close to the antenna, thus contributing to reducing the size of the radio apparatus.

CITATION LIST

PATENT LITERATURE

[0005] [Patent Document No. 1] Japanese Laid-Open Patent Publication No. 2012-253588

SUMMARY OF INVENTION

TECHNICAL PROBLEM

[0006] However, where λ denotes the wavelength of the radio wave to be used, with the radio apparatus of Patent Document 1, since the connection pattern used as the antenna needs to have a length approximate to an integer multiple of λ/2, there needs to be a large space to place the connection pattern between the main board and the metal device, thereby resulting in a large radio apparatus. For example, where the frequency of the radio wave to be used is 500 MHz, the connection pattern needs to have a length approximate to an integer multiple of 30 centimeters, and there is a need to provide a space therefor between the main board and the metal device, thereby resulting in a large radio apparatus.

[0007] The present invention provides a small radio apparatus having a high-efficiency antenna property.

SOLUTION TO PROBLEM

[0008] A radio apparatus in one embodiment of the present invention includes: an antenna for transmitting and receiving radio waves of a wavelength λ; a circuit board connected to the antenna; a power supply; and a conductive line for connecting together the circuit board and the power supply, wherein a sum of a length of the antenna, a length of the circuit board and a length of the conductive line is about λ/2.

ADVANTAGEOUS EFFECTS OF INVENTION

[0009] With a radio apparatus in one embodiment of the present invention, the sum of the length of the antenna, the length of the circuit board and the length of the conductive line is about λ/2. With a radio apparatus in one embodiment of the present invention, the antenna, the circuit board and the conductive line together function as a whole as an antenna. With the circuit board and the conductive line, which connects together the circuit board and the power supply, functioning as a part of the antenna, it is possible to reduce the size of the radio apparatus. Even if the length of the antenna and the circuit board is short, it is possible to realize a high-efficiency antenna property by adjusting the length of the conductive line. For example, it is possible to realize a high-efficiency antenna property as long as the length of the antenna, the circuit board and the conductive line together as a whole satisfies λ/2.

BRIEF DESCRIPTION OF DRAWINGS

[0010] 

[FIG. 1] A diagram showing a radio apparatus according to a first embodiment of the present invention.

[FIG. 2] A diagram showing an antenna according to the first embodiment of the present invention.

[FIG. 3] A diagram showing a circuit board according to the first embodiment of the present invention.

[FIG. 4] A diagram showing a battery according to the first embodiment of the present invention.

[FIG. 5] A diagram showing the antenna current distribution according to the first embodiment of the present invention, where the total length of the antenna, the circuit board and the conductive line is set to λ/2.

[FIG. 6] A graph showing the antenna radiation efficiency according to the first embodiment of the present invention, where the total length of the antenna, the circuit board and the conductive line is varied.

[FIG. 7] A diagram showing a radio apparatus according to a second embodiment of the present invention.

[FIG. 8] A diagram showing a passive component according to the second embodiment of the present invention.

[FIG. 9] A diagram showing a passive component according to the second embodiment of the present invention.

[FIG. 10] A graph showing the antenna radiation efficiency according to the second embodiment of the present invention, where the connection status of the conductive line for supplying the power from the battery is varied.

DESCRIPTION OF EMBODIMENTS

[0011] A radio apparatus in one embodiment of the present invention includes: an antenna for transmitting and receiving radio waves of a wavelength λ; a circuit board connected to the antenna; a power supply; and a conductive line for connecting together the circuit board and the power supply, wherein a sum of a length of the antenna, a length of the circuit board and a length of the conductive line is about λ/2. Thus, the radio apparatus as a whole functions as a dipole antenna, and it is possible to radiate electromagnetic waves from the entirety of the radio apparatus.

[0012] In one embodiment, the length of the antenna is about λ/4. Then, the current value is at maximum at the feeding point for supplying the power from the circuit board to the antenna, and the radio apparatus as a whole resonates, making it possible to efficiently radiate electromagnetic waves.

[0013] In one embodiment, a sum of the length of the circuit board and the length of the conductive line is about λ/4. Then, the current value is at maximum at the feeding point for supplying the power from the circuit board to the antenna, and the radio apparatus as a whole resonates, making it possible to efficiently radiate electromagnetic waves.

[0014] In one embodiment, the power supply is a battery; the conductive line is a conductive line extending from the battery; and the connection to the circuit board is made via a connector provided on the conductive line. By allowing the conductive line extending from the battery to function as a part of the antenna, it is possible to reduce the size of the radio apparatus.

[0015] In one embodiment, a ground is provided on the circuit board; and the length of the circuit board is a length of the ground between a position at which the circuit board and the antenna are connected together and another position at which the circuit board and the conductive line are connected together. In one embodiment, the circuit board is rectangular; and the length of the circuit board is a length of a long side of the circuit board. By allowing the circuit board, together with the conductive line, to function as a part of the antenna, it is possible to reduce the size of the radio apparatus.

[0016] In one embodiment, an area of the circuit board is less than or equal to one half of an area of the antenna. With the configuration of the embodiment of the present invention, the area of the circuit board can be made smaller than the area of the antenna, and it is therefore possible to reduce the size of the radio apparatus.

[0017] In one embodiment, the antenna is a plate-shaped inverted-F antenna, and the length of the antenna is a length that is one half of a perimeter length of the antenna. For example, as the sum of the length of such an antenna, the length of the circuit board and the length of the conductive line is set to about λ/2, the radio apparatus as a whole functions as a dipole antenna, and it is possible to radiate electromagnetic waves from the entirety of the radio apparatus.

[0018] In one embodiment, a positive-pole side of the conductive line is unconnected for high frequencies. Then, the antenna current, which has been offset between the positive-side line and the negative-side line of the conductive line, now flows in one direction, thereby further enhancing electromagnetic waves to be radiated, and it is possible to further improve the antenna efficiency.

[0019] In one embodiment, the radio apparatus further includes a passive component for cutting off a high-frequency signal component on a positive-pole side of the conductive line. For example, the passive component cuts off a signal component whose frequency is c/λ (c is a propagation velocity of electromagnetic waves). For example, the passive component includes an inductor. For example, the passive component includes an inductor and a capacitor connected in parallel to the inductor. As the radio apparatus includes such a passive component, the antenna current, which has been offset between the positive-side line and the negative-side line of the conductive line, now flows in one direction, thereby further enhancing electromagnetic waves to be radiated, and it is possible to further improve the antenna efficiency.

[0020] A radio apparatus in one embodiment of the present invention includes: an antenna for transmitting and receiving radio waves of a wavelength λ; and a circuit board connected to the antenna, wherein a sum of a length of a conductive line for supplying power from a power supply to the circuit board, a length of the circuit board and a length of the antenna is about λ/2. Thus, the radio apparatus as a whole functions as a dipole antenna, and it is possible to radiate electromagnetic waves from the entirety of the radio apparatus.

[0021] In one embodiment, the length of the antenna is about λ/4. Then, the current value is at maximum at the feeding point for supplying the power from the circuit board to the antenna, and the radio apparatus as a whole resonates, making it possible to efficiently radiate electromagnetic waves.

[0022] Embodiments of the present invention will now be described with reference to the drawings. Note that the following embodiments are illustrative, but not limiting, of the present invention.

(Embodiment 1)

[0023] FIG. 1 is a diagram showing a radio apparatus 100 according to a first embodiment of the present invention. The radio apparatus 100 includes an antenna 1 for transmitting and receiving radio waves of a wavelength λ, a circuit board 2 connected to the antenna 1, a power supply 4, a conductive line 3 for connecting together the circuit board 2 and the power supply 4, and a resin housing 10.

[0024] The antenna 1 is, for example, an antenna of an inverted-F type, and has a plate-shaped antenna structure as shown in FIG. 1. Note however that the antenna used in the present invention is not limited to those of the inverted-F type, but may be those of a monopole type or an inverted-L type, for example. The antenna of the present embodiment may be any of various types of antennas such as linear antennas, plate-shaped antennas and planar antennas.

[0025] The circuit board 2 includes thereon a radio section 22 (FIG. 7) for transmitting and receiving electromagnetic waves, and a microcomputer 21 (FIG. 7) for controlling the radio section 22, and also includes thereon a connection terminal 8 for supplying the power from the power supply 4 to those electronic components. The antenna 1 is connected to a feeding point 5 on the circuit board 2 via a feeder line 6, and is connected to the ground of the circuit board 2 via a short-circuit line 7.

[0026] The conductive line 3 is a sheathed conductive line connected to the power supply 4, with a connector 13 (FIG. 4) provided at the distal end thereof for the connection with the circuit board 2.

[0027] The power supply 4 is a battery, for example. The battery 4 is, for example, a package of a plurality of lithium cells connected in parallel, and the conductive line 3 extends from the positive side and from the negative side of one of the cells. The present embodiment uses the battery 4 packaged together with the conductive line 3 having the connector 13 (FIG. 4) provided at the distal end thereof. With the connector 13 connected to the terminal 8 of the circuit board 2, power is supplied to the circuit board 2. Note that while the battery 4 of the present embodiment shown in FIG. 1 includes five lithium cells, this configuration is illustrative, and the present invention may use any type and any number of battery cells. For example, dry cells may be used instead of lithium cells.

[0028] The resin housing 10 is made of a nonmetallic material such as an AES resin or an ABS resin.

[0029] The present embodiment is directed to a radio apparatus including the antenna 1, the circuit board 2 having a length of λ/4 or less, and the battery 4 provided together with the conductive line 3, wherein the antenna 1, the circuit board 2 and the conductive line 3 function together as an antenna, thereby producing a high-efficiency antenna property, by adjusting the total length of the antenna 1, the circuit board 2 and the conductive line 3.

[0030] The length of each element will be described. FIG. 2 is a diagram showing the antenna 1 of the present embodiment. Where the antenna 1 is a plate-shaped inverted-F antenna, the length of the antenna 1 is equal to one half of the perimeter length of the antenna 1. For example, where the antenna 1 is a rectangular inverted-F antenna as shown in FIG. 2, the length of the antenna 1 is the sum of the long side length La and the short side length Lb.

[0031] FIG. 3 is a diagram showing the circuit board 2. The circuit board 2 includes conductors 12, functioning as the ground, provided in a predetermined pattern. The feeding point 5 and the terminal 8 of the circuit board 2 are electrically connected together via the ground 12. The length of the circuit board 2 in the present embodiment is the length of the ground 12 between the feeding point 5 to the antenna 1 and the terminal 8. In other words, the length of the circuit board 2 is equal to the length of the ground 12 from the feeding point 5 to the conductive line 3. The length of the ground 12 contributes to the antenna property. Where the feeding point 5 and the terminal 8 are connected together along a straight line by the ground 12, the length Lc of the straight line is the length of the circuit board 2. Where the feeding point 5 and the terminal 8 are connected together along a detour-route pattern of the ground 12, the length of the detour-route pattern of the ground 12 is the length of the circuit board 2. Where the circuit board 2 is rectangular and the feeding point 5 and the terminal 8 are provided near the apposite ends in the long side direction, as in the example of FIG. 3, the length of the circuit board 2 can be said to be the length of the long side of the circuit board 2.

[0032] FIG. 4 is a diagram showing the battery 4. The conductive line 3 extends from the body part of the battery 4, in which a plurality of lithium cells are arranged in parallel, and the length Lc of the conductive line 3 is the length of the conductive line 3 contributing to the antenna property. Note that where the size of the connector 13 to be connected to the terminal 8 of the circuit board 2 is large, the length of the connector 13 may be included in the length of the conductive line 3. Where an electronic component is provided along the conductive line 3, the electronic component may also be included in the length of the conductive line 3.

[0033] Although the positive-side line and the negative-side line of the conductive line 3 are designed to have substantially the same length, if their lengths are different from each other, the longer line contributes to the antenna property. Note that the length of the battery body part (lithium cell part) does not contribute to the antenna property.

[0034] While the antenna 1, the circuit board 2 and the battery 4 need to be designed with dictated dimensions to some degree as they have a substantial influence on the exterior design and the performance of the product, the antenna property substantially varies depending on these dimensions.

[0035] In view of this, the antenna 1, the circuit board 2 and the conductive line 3 of the battery 4 are allowed to together function as a whole as an antenna, so that it is possible to reduce the size of the radio apparatus 100 and to realize a high-efficiency antenna property.

[0036] Particularly, where λ denotes the wavelength of the radio wave to be used, if the length of the antenna 1 is set to about λ/4 and the sum of the length of the circuit board 2 and the length of the conductive line 3 is set to about λ/4, the apparatus operates as if it were a λ/2 dipole antenna.

[0037] FIG. 5 shows the distribution of the antenna current amplitude where each element of the radio apparatus 100 is formed with the dimension described above. Since the antenna 1, the circuit board 2 and the conductive line 3 of the battery 4 apparently form a λ/2 dipole antenna, the antenna current amplitude thereof is as shown by an antenna current distribution 30 of FIG. 5. There is zero current at the distal end of the antenna 1 and the battery 4, since they are open-ended, and the amplitude of the antenna current is at maximum in the vicinity of the feeding point 5 on the circuit board 2 to the antenna 1. That is, there is a resonance phenomenon, and one can expect a high-efficiency antenna property.

[0038] Therefore, by adjusting the length of the conductive line 3 so as to apparently realize a λ/2 dipole antenna, it is possible to improve the antenna property.

[0039] FIG. 6 shows the antenna radiation efficiency where the length of the conductive line 3 is varied while the length of the antenna 1 and the length of the circuit board 2 are fixed.

[0040] Where the antenna 1 having a length of λ/4 was used, and the total length of the circuit board 2 and the conductive line 3 was set to λ/4 by adjusting the length of the conductive line 3, the total length was λ/2 and an antenna radiation efficiency of -3.6 dB was realized.

[0041] Where the total length including the antenna 1 was set to λ/3, the antenna radiation efficiency was -9 dB as there was no resonance phenomenon.

[0042] Thus, it is possible to realize a high-efficiency antenna property by setting the total length, which is the sum of the length of the antenna 1, the length of the circuit board 2 and the length of the conductive line 3, to about λ/2.

[0043] Typically, with a radio apparatus using an antenna of an inverted-F type, the area of the circuit board is larger than the area of the antenna. In contrast, in the present embodiment, the area of the circuit board 2 can be made smaller than the area of the antenna 1, and it is therefore possible to reduce the size of the radio apparatus 100. For example, the area of the circuit board 2 can be made one half or less of the area of the antenna 1.

(Embodiment 2)

[0044] FIG. 7 is a diagram showing a radio apparatus 100 according to a second embodiment of the present invention. FIG. 8 is a diagram showing a passive component 23 provided on the circuit board 2. Due to the passive component 23, the positive-side line of the conductive line 3 of the present embodiment is apparently unconnected for a high frequency band or for particular frequencies, thereby realizing a higher-efficiency antenna property.

[0045] The passive component 23 includes an inductor 25, for example. The passive component 23 is, for example, connected between the microcomputer 21 and the terminal 8 on the circuit board 2. In this case, power may be supplied to the radio section 22 via the microcomputer 21. The passive component 23 may be connected between the radio section 22 and the terminal 8, in which case power may be supplied to the microcomputer 21 via the radio section 22. The passive component 23 may be connected to the terminal 8, and the microcomputer 21 and the radio section 22 may be connected to the passive component 23 via lines extending from the passive component 23 to the microcomputer 21 and to the radio section 22. Note that the microcomputer 21 and the radio section 22 may be formed as an integral unit. The passive component 23 is connected to the positive-side line of the conductive line 3 to cut off high-frequency signal components along the positive-side line of the conductive line 3. For example, the passive component 23 cuts off signal components whose frequency is c/λ. Herein, c is the propagation velocity of electromagnetic waves. That is, the passive component 23 cuts off signal components having the frequency of the radio wave to be used.

[0046] Where f denotes the frequency and L denotes the inductor value, the impedance Z of the inductor 25 is expressed as shown in Expression 1 below.
[Exp. 1]

[0047] By selecting the inductor 25 so as to produce such a high impedance that makes it look like as if the circuit board 2 side were unconnected at a frequency to be cut off, it is possible to cut off signal components of the frequency to be cut off, and it is possible to realize a high-efficiency antenna property.

[0048] As shown in FIG. 9, the passive component 23 may include the inductor 25 and a capacitor 26 connected in parallel to the inductor 25. Also with such a circuit configuration, it is possible to cut off high-frequency signal components on the positive-side line of the conductive line 3 and to increase the antenna efficiency, as described above.

[0049] Now, where C denotes the capacitor value, the relationship between the frequency f, the inductor value L and the capacitor value C is expressed as shown in Expression 2 below.
[Exp. 2]

[0050] By selecting the inductor value L and the capacitor value C so that the frequency f is equal to the frequency to be cut off, it is possible to cut off signal components of the frequency to be cut off, and it is possible to realize a high-efficiency antenna property.

[0051] Where the positive-side line of the conductive line 3 is connected, for high frequencies, to the circuit board 2, the antenna current flowing therethrough functions to offset the current flowing through the negative-side line of the conductive line 3, thereby adversely affecting the antenna property.

[0052] FIG. 10 is a graph showing the antenna efficiency when the positive-side line of the conductive line 3 is connected for high frequencies and the antenna efficiency when it is unconnected, where the antenna 1 having a length of λ/4 is used.

[0053] When the circuit board 2 was connected, for high frequencies, to the positive-side line of the conductive line 3, the antenna efficiency was -10 dB.

[0054] On the other hand, when the inductor 25 was inserted between the microcomputer 21 and/or the radio section 22 on the circuit board 2 and the positive-side line of the conductive line 3 so as to make it look as if it were apparently unconnected for the frequency to be used, the antenna efficiency was -5.3 dB, indicating an improvement of the antenna efficiency by 4.7 dB as compared with a case where it was connected for high frequencies.

[0055] The configuration of an embodiment of the present invention is particularly applicable when the wavelength λ of the radio wave to be used is long. For example, where λ=500 MHz, λ/2 is about 30 centimeters, and the resin housing 10 will physically become large when one attempts to attain λ/2 for the antenna 1 and the circuit board 2. However, according to an embodiment of the present invention, the same capacity can be attained by setting the length of the antenna 1 to λ/4 (about 15 centimeters) and the sum of the lengths of the circuit board 2 and the conductive line 3 of the battery 4 to λ/4, thus realizing a reduction in the size of the resin housing 10 by about 30% as compared with the former configuration.

[0056] The radio apparatus 100 according to an embodiment of the present invention can realize a high-efficiency antenna property by adjusting the length of the conductive line 3 even if the length of the circuit board 2 is short. Since the circuit board 2 and the conductive line 3 are allowed to function as a part of the antenna, it is possible to reduce the size of the radio apparatus 100.

[0057] According to an embodiment of the present invention, even if the radio apparatus 100 is small, the entirety of the radio apparatus 100 is allowed to function as an antenna, thereby realizing a high-efficiency antenna capacity. With the antenna 1, the circuit board 2 and the conductive line 3 functioning as a whole as an antenna, it is possible to produce a high-efficiency antenna property. As the dimensions of the antenna 1 and the circuit board 2 are dictated by the characteristics of particular products, it is possible to realize a high-efficiency antenna capacity by adjusting the length of the conductive line 3, particularly by setting the total length to λ/2. With the antenna 1, the circuit board 2, and the conductive line 3 functioning as a whole as an antenna, it is possible to reduce the size of the radio apparatus 100.

INDUSTRIAL APPLICABILITY

[0058] The present invention is particularly applicable in technical fields where there is a demand for reducing the size of a radio apparatus.

REFERENCE SIGNS LIST

[0059] 

1

Antenna

2

Circuit board

3

Conductive line

4

Battery

10

Resin housing

23

Passive component

100

Radio apparatus

Claims

1. A radio apparatus comprising:

an antenna for transmitting and receiving radio waves of a wavelength λ;

a circuit board connected to the antenna;

a power supply; and

a conductive line for connecting together the circuit board and the power supply,

wherein a sum of a length of the antenna, a length of the circuit board and a length of the conductive line is about λ/2.

2. The radio apparatus according to claim 1, wherein the length of the antenna is about λ/4.

3. The radio apparatus according to claim 1 or 2, wherein a sum of the length of the circuit board and the length of the conductive line is about λ/4.

4. The radio apparatus according to any one of claims 1 to 3, wherein:

the power supply is a battery;

the conductive line is a conductive line extending from the battery; and

the connection to the circuit board is made via a connector provided on the conductive line.

5. The radio apparatus according to any one of claims 1 to 4, wherein:

a ground is provided on the circuit board; and

the length of the circuit board is a length of the ground between a position at which the circuit board and the antenna are connected together and another position at which the circuit board and the conductive line are connected together.

6. The radio apparatus according to any one of claims 1 to 5, wherein:

the circuit beard is rectangular; and

the length of the circuit board is a length of a long side of the circuit board.

7. The radio apparatus according to any one of claims 1 to 6, wherein an area of the circuit board is less than or equal to one half of an area of the antenna.

8. The radio apparatus according to any one of claims 1 to 7, wherein the antenna is a plate-shaped inverted-F antenna, and the length of the antenna is a length that is one half of a perimeter length of the antenna.

9. The radio apparatus according to any one of claims 1 to 8, wherein a positive-pole side of the conductive line is unconnected for high frequencies.

10. The radio apparatus according to any one of claims 1 to 9, further comprising a passive component for cutting off a high-frequency signal component on a positive-pole side of the conductive line.

11. The radio apparatus according to claim 10, wherein the passive component cuts off a signal component whose frequency is c/A (c is a propagation velocity of electromagnetic waves).

12. The radio apparatus according to claim 10 or 11, wherein the passive component includes an inductor.

13. The radio apparatus according to claim 10 or 11, wherein the passive component includes an inductor and a capacitor connected in parallel to the inductor.

14. A radio apparatus comprising:

an antenna for transmitting and receiving radio waves of a wavelength λ; and

a circuit board connected to the antenna,

wherein a sum of a length of a conductive line for supplying power from a power supply to the circuit board, a length of the circuit board and a length of the antenna is about λ/2.

15. The radio apparatus according to claim 14, wherein the length of the antenna is about λ/4.

Drawing